Reflection type liquid crystal display device and manufacturing method thereof

A reflection panel prototype was fabricated under the following fabrication conditions.

Photo-sensitive resin: LC-200 (general purpose resist made by Shipley Co.)

Using a spinner, the above mentioned photo-sensitive resin material was rotated for 3 seconds at 350 rpm, then rotated for 20 seconds at 800 rpm to form the resin layer.

Pre-bake: 30 minutes at 90° C.

Film thickness was changed by exposing the entire surface of the panel.

Post bake: 40 minutes at 120° C.

UV curing: Using a UV irradiation device made by ORC, UV was irradiated on the entire surface of the resin layer at 5200 mJ/cm²(measured by a UV25 sensor made by ORC).

Resist final bake: 40 minutes at 200° C.

Reflection material: Al with a 200 nm film thickness (deposited by resistance heating)

A liquid crystal panel was fabricated using a reflection electrode fabricated under the above mentioned conditions, and reflection characteristics were evaluated using an integrating sphere. As a result, as FIG. 9 shows, it was determined that a reflection liquid crystal panel with better reflection characteristics than prior art was implemented.

Fabrication example 2 can be applied to the case when pattern exposure is executed.

The following fabrication conditions are when the photo-sensitive resin is half-exposed and the pattern sags by heat, in order to form a reflection electrode having the desired reflection characteristics. When this system is applied to a TFT substrate, exposure is required twice, but resin formation can be only once. However, the problem is that reflection characteristics greatly depend on the exposure conditions and heat sagging conditions. To alleviate this problem, we invented a method of adding a micro-groove formation process to the half exposure process. The fabrication conditions are as follows.

Photo-sensitive resin: LC-200 (general purpose resist made by Shipley Co.)

3 seconds at 350 rpm first, then 20 seconds at 800 rpm using a spinner.

Pre-bake: 30 minutes at 90° C.

Using photo-masks (having an octagon, square, cross, pentagon, doughnut, triangle, ellipse, sector, figure eight shapes, and an area without a pattern. Here the area without a pattern is an area where only micro-grooves are formed), contact exposure was executed (under the same exposure conditions) using a large exposure system.

Development process: 50 seconds

Post-bake: 40 minutes at 120° C.

UV curing: 5200 mJ/cm²(micro-groove forming conditions)

UV curing: 1300 mJ/cm²(micro-groove non-forming conditions, prevents sagging by heat), optimized under half exposure conditions

Resist final bake: 40 minutes at 200° C.

Reflection material: Al at a 200 nm film thickness (deposited by resistance heating)

A liquid crystal panel was fabricated using a reflection electrode formed under the above mentioned conditions, and the reflection characteristics were evaluated using an integrating sphere. As a result, as FIG. 15 shows, it was determined that a reflection panel having stable and high reflection characteristics can be fabricated by adding micro-groove formation conditions to the half exposure system. However, only the area where only micro-grooves are formed on the part with no pattern formation showed the highest reflection characteristics.

In fabrication example 3, it was discovered that when micro-grooves are formed on a flat substrate, uniformity from a macro-view improves if the surface of the resin is separated into blocks by half exposure, compared with the case of not separating into blocks, as shown in FIG. 18.

FIG. 59 shows micro-photographs depicting an example of micro-groove formation when block separation was performed by half exposure.

As FIG. 59 shows, wrinkles of micro-grooves are confined to a block. In other words, it is known that micro-grooves can be separated by half exposure. It was also discovered that the shape of micro-grooves can be controlled by block shape and depth of separation (exposure conditions).

CONCRETE FABRICATION EXAMPLES

In the block separation shown in fabrication example 3, it was discovered that it is not necessary to form block separation on the surface of the resin layer by half exposure, but that micro-grooves can be separated or that shape thereof can be controlled by creating film thickness distribution on the photo-sensitive resin by forming undulation on the substrate surface. In other words, film thickness distribution is created on the photo-sensitive resin layer by a data bus line, gate line and auxiliary electrode Cs line on the substrate shown in FIGS. 16 and 17, by which blocks of micro-grooves are separated.

FIG. 60 is a micro-photograph showing the micro-grooves formed in fabrication example 4.

Here, AFP 750 (made by Clariant Japan) is coated on a TFT substrate, pre-bake is performed, a contact hole is exposed using a stepper, the resist is developed, and post-bake is performed for 80 minutes at 135° C., then UV is irradiated at 2600 mJ/cm²for UV curing, and final bake is performed on the resist at 200° C. for 60 minutes, to form the micro-grooves.

As FIG. 60 shows, micro-grooves are separated on the data bus, gate line and Cs line, which are the composing elements on the substrate. This is because resist film thickness decreases on the data bus, gate line and Cs line, and micro-grooves are separated.

FIG. 61 is a micro-photograph of one polarizer type TFT driven reflection liquid crystal device fabricated using a TFT substrate and CF substrate, where an Al electrode is formed by sputtering and a pixel electrode is formed by separation by photo-lithography.

As FIG. 61 shows, micro-grooves are deformed not only on the data bus, gate line and Cs line but also near the contact hole. This indicates that bump shapes on the reflection electrode surface can be controlled by the size, shape, arrangement and number of contact holes.

Table 1 shows the characteristics comparison between an actually fabricated reflection panel and reflection panels made by other companies.

As Table 1 shows, the fabricated reflection panel exhibits higher reflection characteristics than other companies, both in the 30° incident system using a point light source and in measurement by an integrating sphere using a diffuse light source.

TABLE 1

Reflectance comparison with reflection LCDs made by
other companies (reflector of a 100% white display)
Measurement system	Company A	Company B	Present Invention

30° incident	18	18	35
Integrating sphere	11	14	16

The 30° incidence indicates reflectance (standard white panel: 100%) at the front face of the panel under a 30° incident point light source, and the integrating sphere indicates reflectance (standard white panel: 100%) at the front face of the panel under a uniform diffuse light source with full attachment.

Fabrication Example 5

The shape of the micro-grooves can be controlled by controlling the arrangement and shape of the electrode layer and the inter-layer insulation film layer of the gate electrode, Cs electrode (same layer as the gate electrode) and the data electrode, which are the composing elements of a TFT substrate.

FIG. 62 shows plan views depicting examples of the TFT substrate. FIG. 62A shows a normal TFT substrate where a gate electrode 131, Cs electrode 132, data electrode 133 and TFT element 134 are formed. FIG. 62B is an example when two lines of linear structures 136 are formed in a diagonal direction during patterning of the gate electrode 131 and Cs electrode 132, in addition to the normal TFT structure. FIG. 62C is an example when n number of circular structures 137 are formed in the same way as FIG. 62B, FIG. 62D is an example when two lines of linear structures 136 are formed in parallel with the data electrode 133, FIG. 62E is an example when two circular structures 137 are formed just like FIG. 62C, FIG. 62F is an example when n number of linear structures 136 are formed in parallel with the data electrode 133, and n number of linear structures 136 are formed in parallel with the gate electrode 133, and FIG. 62G is an example when four linear structures 136 are formed in the diagonal direction. The photo-sensitive resin layer is formed on the structure shown in the above mentioned plan views, and micro-grooves are formed on the surface.

As illustrated, wrinkle shapes of the micro-grooves generated on the surface of the photo-sensitive resin can be controlled by forming structures using these materials so as to create step differences in the pixel area when each constituting element of the gate electrode 131, Cs electrode 132 (the same layer as the gate electrode 131) and data electrode 133 are formed. In this case, the structures are patterned at the same time with each constituting element, so the number of processing steps are unchanged. Because of this, it is possible to add directivity to the reflection characteristics and to control alignment of the liquid crystal layer by the micro-groove azimuth.

Fabrication Example 6

Micro-grooves can be controlled in the same way by forming the step difference shape of fabrication example 5 by selectively etching the TFT structure.

Fabrication Example 7

Bump shapes at the surface of the reflection electrode can be controlled by the size, shape, arrangement and number of contact holes for electrically connecting the drain electrode (the same layer as the data electrode) of the TFT substrate and the reflection electrode. In other words, by forming a plurality of contact holes to be a predetermined shape in a pixel, undulation can be formed on the photo-sensitive resin layer and the wrinkle shape of the micro-grooves formed on the surface can be controlled.

FIG. 63 shows examples. FIG. 63A shows a plan view of a normal TFT substrate where the gate electrode 131, Cs electrode 132, data electrode 133, TFT element 134 and contact hole 138 are formed. FIGS. 63B, 63E, 63F are examples when the number of contact holes 138 are changed, and FIGS. 63C, 63D, 63G and 63H are examples when the shape of the contact holes 138 are changed. In these examples, the source electrode 18 shown in FIG. 2 is formed on the entire face of a pixel block, and a plurality of contact holes CH are formed thereon. The wrinkle shapes of the micro-grooves are formed with contacts hole CH as the center.

As FIG. 63 shows, the micro-grooves generated on the surface of the photo-sensitive resin can be controlled by controlling the size, shape, arrangement and number of the contact holes 138.

Fabrication Example 8

It has been confirmed that the liquid crystal aligns along the groove on the surface of the reflection electrode where the micro-grooves of the present invention are formed, and by using this characteristic, a random alignment type reflection liquid crystal display device can be implemented without performing special alignment processing, such as rubbing processing on the alignment film, in the horizontal alignment, vertical alignment and hybrid alignment (HAN), and the panel formation process can be simplified.

As described above, according to the present embodiment, process simplification, yield improvement, and a decrease in manufacturing cost can be implemented, a reflection electrode which can stably implement high reflection characteristics can be formed, and a reflection liquid crystal display device with high reliability whereby a high brightness display is possible can be implemented.

[Modified Process of Micro-Groove 2]

A rough configuration of the reflection liquid crystal display device of the present embodiment is the same as the configuration shown in FIG. 2.

The main point of the present embodiment is that when undulation is formed on the surface of the resin layer by performing heat treatment on the resin layer, a part which thermal deformation characteristics are different from the resin is created in the resin layer, or a material which thermal deformation characteristics are different from the resin is mixed into the resin layer, so as to control the bump shape of the micro-grooves to be a desired shape.

Specifically, suitable methods include a method of dispersing particles which have different thermal deformation characteristics into the resin layer, a method of forming the above mentioned part by layering another resin layer having different thermal deformation characteristics in the resin layer, a method of forming the above mentioned part by forming another resin layer having different thermal deformation characteristics in the resin layer into a predetermined shape using a pattern, and a method of forming the part having different thermal deformation characteristics by performing partial processing (e.g. irradiating energy rays selectively onto the resin layer or changing the irradiation intensity of the energy ray). The bump shape of the resin layer is controlled such that the ridge line shape becomes at least one of a line, curve, loop and branch shape.

As FIG. 64 shows, novolak photo-sensitive resin 102, where SiO₂particles 103 with about a 1 μm diameter are dispersed, is coated on the glass substrate 101, a post bake is performed at 160° C., then UV is irradiated at an irradiation energy equal to or higher than image exposure condition, so as to form an area with different thermal deformation characteristics in the photo-sensitive resin 102. Then heat treatment is performed a temperature equal to or higher than a post bake temperature, so as to form fine wrinkled undulation 104 on the surface of the photo-sensitive resin 102 with the particles 103 having different thermal deformation characteristics as cores. And a reflection layer (not illustrated) such as Al is formed on the photo-sensitive resin 102, so as to fabricate a reflector having a surface which reflects the shape of the undulation 104.

In this example, silicon dioxide particles having different thermal deformation characteristics are dispersed in the photo-sensitive resin layer, and a distribution having different thermal deformation characteristics is formed in the photo-sensitive resin layer by UV exposure. It was discovered that finer wrinkle shapes are formed after heat treatment is performed compared with the case when silicon dioxide particles were not dispersed.

As FIG. 65 shows, a layer 105 having thermal deformation characteristics different from the photo-sensitive resin 102 is layered in the photo-sensitive resin 102. After post baking at 160° C., UV is irradiated at irradiation energy equal to or higher than image exposure conditions, so as to form an area having different thermal deformation characteristics in the photo-sensitive resin 102. Then heat treatment is executed at a post bake temperature or higher. As a result, finer wrinkle undulation 104 is formed on the surface of the photo-sensitive resin 102 because the thermal deformation characteristics of each layer are different. Then the reflection layer (not illustrated) such as Al is formed on the photo-sensitive resin 102, so as to fabricate a reflector having a surface which reflects the shape of the undulation 104.

As FIG. 66 shows, a resin 106 having thermal deformation characteristics different from the photo-sensitive resin 102 is formed on the substrate 101 by patterning, and is covered by the photo-sensitive resin layer 102. To prevent diffraction, the pattern shapes are preferred to be random. After post-bake is executed at 160° C., UV is irradiated at an irradiation energy equal to or higher than the image exposure conditions, so as to form an area having different thermal deformation characteristics from the photo-sensitive resin 102 in the photo-sensitive resin 102. Then heat treatment is performed at a post-bake temperature or higher, and as a result, finer wrinkled undulation 104 are formed on the surface of the photo-sensitive resin 102, because the thermal deformation characteristics of each layer are different. Then a reflection layer (not illustrated), such as A1, is formed on the photo-sensitive resin 102, so as to fabricate a reflector having a surface which reflects the shape of the undulation 104.

CONCRETE FABRICATION EXAMPLES

As FIG. 67 shows, UV is selectively irradiated on the photo-sensitive resin, so as to form an area 107 having different thermal deformation characteristics. After post baking at 160° C., UV is irradiated on the entire surface at a irradiation energy equal to or higher than the image exposure conditions, so as to form an area having different thermal deformation characteristics in the photo-sensitive resin 102. Then heat treatment is performed at a post bake temperature or higher, and as a result, finer wrinkled undulation 104 are formed on the surface of the photo-sensitive resin 102, because the thermal deformation characteristics of each layer are different. Then a reflection layer (not illustrated), such as Al, is formed on the photo-sensitive resin 102, so as to fabricate a reflector having a surface which reflects the shape of the undulation 104.

As described above, according to the present embodiment, the roughness of the display screen is controlled by meticulously controlling the wrinkled undulation on the surface of the photo-sensitive resin, and a simplification of process, improvement of yield and decrease in manufacturing cost can be implemented, and a reflection type liquid crystal display device with high reliability, which can display with high lightness, can be implemented by forming a reflection electrode which can stably implement high reflection characteristics.

In the above example, the process of irradiating UV on the entire surface can be omitted if material having different thermal deformation characteristics is mixed, layered or distributed in the photo-sensitive resin layer.

[Modified Process of Micro-groove 3]

A rough configuration of the reflection liquid crystal display device of the present embodiment is the same as the configuration shown in FIG. 2.

The main point of the present embodiment is that when thermal characteristics distribution is created in the resin layer, the distribution of the shrinkage factor or the expansion factor is created in the thickness direction of the resin layer by irradiating the light with a predetermined exposure energy on the surface of the resin layer, so as to control the bump shape of the resin layer. Specifically, it is preferable to set the exposure energy to be 1000 mJ/cm²or higher value.

Resist having a different shrinkage factor is layered on the glass substrate 201 as a resin layer, and is baked at 200° C. for 60 minutes, then it was examined how undulation (micro-grooves) are generated on the resist surface. Examination showed that undulation (micro-grooves) were generated on the surface when the layer 203, having a small shrinkage factor, is formed on a layer 202 having a large shrinkage factor, as shown in FIG. 68, but the undulation (micro-grooves) were not generated when the layer 202, having a large shrinkage factor, is formed on the layer 203 having a small shrinkage factor.

The reason follows. As FIG. 69 shows, stress generated in the layer 202 with a large shrinkage factor at the bottom layer influences the layer 203 with a small shrinkage factor at the top layer, and deformation is generated in the layer 203 with a small shrinkage factor at the top layer. If the layer 203 with a small shrinkage factor is at the bottom, little stress is generated, and the top layer 202 with a large shrinkage factor is not influenced, so deformation by heat treatment is not generated and micro-grooves are not formed.

Therefore when two types of photo-sensitive resin layers with different thermal shrinkage factors are layered, it is necessary to form a resist with a high thermal shrinkage factor at the bottom layer and a resist with a low thermal shrinkage factor at the top layer.

4000 mJ/cm²of UV is irradiated on the novolak photo-resist coated on the glass substrate to cause a cross-link reaction of resist near the surface. The novolak resin near the surface of the resist polymerizes by an oxidation reaction, as shown in FIG. 70 (FIG. 70 is one example of the reaction). Since the polymerized novolak has a smaller shrinkage factor than the non-polymerized novolak, distribution of the shrinkage factors can be formed such that the shrinkage factor is small at the resist surface and the shrinkage factor is large inside the resist.

Therefore by forming a novolak photo-resist layer on the glass substrate and irradiating UV on the entire surface to cross-link the resist at the surface, a structure where the top layer has a small shrinkage factor and the bottom layer has a large shrinkage factor can be created. Micro-grooves can be formed by performing heat treatment at the surface thereafter.

Resist AFP 750 (made by Clariant Japan) is coated on the 0.7 mm thick glass substrate to a 3 μm thickness, and solvent in the resist is evaporated by baking the resist for 30 minutes at 90° C. in a clean oven. UV is then irradiated at 0-6500 mJ/cm². After irradiating UV, the resist was baked for 60 minutes at 200° C. in a clean oven, and the result of observing the shape of the resist by microscope is shown in FIG. 71.

As FIG. 71 shows, undulation (micro-grooves) are generated on the resist surface by irradiating UV at a 2600 mJ/cm²or higher energy.

We examined how undulation is generated on the resist surface by changing the baking temperature (time is fixed to 30 minutes) before UV irradiation and dose of UV. This result is shown in FIG. 72. The black dot indicates a case when micro-grooves were generated, and X indicates a case when micro-grooves were not generated.

As FIG. 72 shows, undulation is generated under specific conditions, that is, when the bake temperature before UV irradiation is 135° C. or less and the dose of UV is 1000 mJ/cm²or more.

FIG. 73 shows the result of examining the state of the generation of undulation when the bake temperature is changed before UV irradiation and after UV irradiation while fixing the dose of UV at 3900 mJ/cm².

The result shows that undulation is generated when the bake temperature before UV irradiation is 135° C. or less and the bake temperature after UV irradiation is higher than that before UV irradiation. However, if the bake temperature before UV irradiation is set to 90° C. or less, bubbles are generated, as the micro-photograph in FIG. 74 shows. This is because the solvent in the resist is not completely evaporated.

Table 2 shows the results when the bake temperature before UV irradiation and bubble generation are examined. As Table 2 shows, bubbles are not generated if the bake temperature before UV irradiation is 90° C. or more. Therefore it became clear that uniform undulation (micro-grooves) without defects, due to bubble generation, can be formed by baking in a 90-135° C. temperature range. If the temperature exceeds 150° C., it is a glass transition temperature or higher where micro-grooves are not formed.

TABLE 2

Bake temperature and bubble generation states before UV
irradiation
	Temperature	Bubble generation	Remarks

	25° C.	Generated
	30° C.	Generated
	50° C.	Generated
	70° C.	Generated
	80° C.	Generated
	90° C.	No
	105° C.	No
	120° C.	No
	135° C.	No
	150° C.	No	No undulation generated

Undulation were examined when the resist film thickness is changed. Resist AFP 750 (30 cP viscosity) is coated on the glass substrate while changing the rotation frequency in an 800-5000 rpm range, and is baked for 30 minutes at 90° C. After baking, UV is irradiated at 3900 mJ/cm², and baking is finally performed for one hour at 200° C.

FIG. 75 shows micro-photographs of undulation (micro-grooves) fabricated as above.

As FIG. 75 shows, the amplitude and cycle of the undulation decreases as the rotation frequency of the spinner increases (as the film thickness of the resist decreases). Even in the case of using resist AFP 750 changing between 40 CP and 15 CP viscosity, we observed a phenomena where film thickness decreased along with a decrease in the amplitude and cycle of undulation.

A reflector was fabricated by depositing aluminum (Al) on the undulation formed at the resist surface to be a 200 nm film thickness. The reflector and 0.7 mm thick glass substrate were optically contacted with immersion oil (1.53 refraction index), and reflection characteristics were measured using an integrating sphere. Since the refraction index of the liquid crystal and the glass substrate are both about 1.5, a reflection type liquid crystal display device can be created virtually by optically contacting the glass substrate on the reflector.

FIG. 76 shows the result of measuring the reflectance.

The abscissa in FIG. 76 is the resist film thickness which was measured using a non-contact three-dimensional shape measurement device (made by Hishiko). As FIG. 76 shows, a 60% or higher reflectance is obtained for resist film thickness in a 1.5-4 μm range. Since reflectance on a newspaper surface is about 60%, a bright reflection liquid crystal display device can be implemented by setting the resist film thickness to 1.5-4 μm. A resist with a different viscosity CD was used to change the resist film thickness.

Fabrication Example 5

Using resists LC-200 and S1808 (both made by Shipley), the generation of undulation was examined, and a result similar to the result of the fabrication example 1 was obtained. In the case of LC-200, S1808 and AFP 750, fine undulation was generated even if the structure of novolak resin in the resist is different, so it was confirmed that undulation can be implemented if the resist is a novolak resin type.

We performed a similar experiment using AFP 750 without a sensitizing agent, and undulation was generated even with a resist without a sensitizing agent. By this, it was confirmed that undulation is generated by a novolak resin and a sensitizing agent in the resist is not necessary for generating undulation.

Fabrication Example 6

Resist AFP 750 is coated on a 0.7 mm thick glass substrate at a 3 μm thickness, baked for 30 minutes at 90° C. in a clean oven, then UV was irradiated at 3900 mJ/cm². After UV irradiation, undulation was fabricated by baking the resist for 60 minutes at 200° C. in a clean oven. A reflector was formed by forming a 300 nm aluminum film on the undulation. Using this fabricated reflector and a glass substrate with a transparent electrode ITO, the liquid crystal cell shown in FIG. 77 was fabricated using a 4 μm diameter spacer.

For the liquid crystal, FT-5045 made by Chisso was used, and, as shown in FIG. 77, a polarizer and ¼ wavelength plate were glued onto the front face of the 0.7 mm thick glass substrate. As a result of observing this liquid crystal cell indoors, it was clear that a good light display was obtained.

When voltage was applied, it was confirmed that a dark state was obtained and the contrast of the light state and dark state is large. FIG. 78 shows the result of measuring reflectance when the applied voltage is changed using an integrated sphere. In FIG. 78, the abscissa is the applied voltage to the cell, and the white display changes to a black display by changing this applied voltage to the cell. As FIG. 78 shows, it was confirmed that a good display with high reflectance (30%) and high contrast (18) was obtained.

Fabrication Example 7

Resist AFP 750 is coated on a 0.7 mm thick glass substrate to be a 3 μm thickness, baked for 30 minutes at 90° C., and UV was irradiated at 32 mJ/cm²using a mask where circular patterns with a 10 μm diameter are arranged at random. After UV irradiation, the resist film was soaked in MF 319 developer so as to form circular patterns. After baking the substrate for 40 minutes at 120° C. to completely evaporate the developer in the resist, UV was irradiated at 1300 mJ/cm²and 2600 mJ/cm². Then the resist was baked for one hour at 200° C. so as to form undulation.

FIG. 79 shows a micro-photograph of a patterned resist substrate after baking. As the photograph shows, fine wrinkled undulation is generated on the circular patterns by UV irradiation. However it was discovered that fine undulation is not generated when the same experiment was performed by increasing the UV dose to 80 mJ/cm²to form circular patterns.

So we examined the UV dose and the micro-pattern generation status during patterning. Table 3 shows the result, and FIG. 80 shows micro-photographs of substrates when 80 mJ/cm²and 35 mJ/cm²are irradiated respectively.

As Table 3 shows, if the first patterning is executed at 60 mJ/cm²or less exposure energy, fine wrinkle shapes are generated to be patterned undulation. This means that if the exposure energy of half exposure during patterning is too high, the undulation formed thereby become deep, and micro-grooves are not easily formed on the surface. Therefore micro-grooves are effectively formed on the surface by forming shallow undulation with a relatively low exposure energy.

TABLE 3

Relationship between UV dose and micro-undulation
(micro-grooves) generation during patterning
UV dose (mJ/cm²)	Generation of micro-undulation

10	Generated
20	Generated
30	Generated
35	Generated
40	Generated
45	Generated
50	Generated
60	Generated
70	Not generated
80	Not generated
100	Not generated

Fabrication Example 8

As FIG. 81 shows, striped undulation 303 (height: 0.5 μm, width: 15 μm) were formed on the glass substrate 301, and resist layer 304 (AFP 750) was coated thereon. After baking for 30 minutes at 90° C., UV at 3900 mJ/cm²was irradiated, and the resist was baked for one hour at 200° C.

FIG. 82 shows micro-photographs of fine micro-groove shapes which are generated after baking.

For comparison, FIG. 82 also shows a micro-photograph of a fine micro-groove shape when undulation is not formed under the resist film. When undulation exist under the resist film, a step difference is formed on the surface of the resist, where the stress applied inside the resist differs, so the fine micro-groove shape becomes different from the peripheral area.

As described above, according to the present embodiment, a simplification of process, improvement of yield and a decrease in manufacturing cost can be implemented, and a reflection liquid crystal display device with high reliability which can display with high lightness can be implemented by forming a reflection electrode which can stably implement high reflection characteristics.

[Control of Inclination Angle Distribution of Reflector]

FIG. 19 is a diagram depicting an actual environment where the reflection type liquid crystal display device based on the present embodiment is used. In the environment where the reflection type liquid crystal display device is used, light sources exist in various locations. Therefore, considering various environments of use, as shown in FIG. 19, it is necessary to assume the case when the reflection type liquid crystal display device is positioned under a uniform diffuse light source placed inside a sphere. Under such a use environment, all incident lights that exist in the solid angle of the half sphere are irradiated into the display panel.

To determine the light intensity L to enter the reflection type liquid crystal display device, X-Y-Z axis, incident angle θ_iand azimuth angle φ_iare defined as shown in FIG. 20. The incident angle θ_iis an angle between the Z axis and incident light, and azimuth angle φ_iis an angle between the incident light and the X axis. If the light intensity per unit area of the sphere shown in FIG. 19 (hereafter integrating sphere) is I(θ_i, φ_i), then the light intensity dL is given by $\begin{matrix} d L = I (θ_{i}, ϕ_{i}) \cdot dw \\ = I (θ_{i}, ϕ_{i}) \cdot ds / r^{2} \end{matrix}$

Here, ω is a solid angle, ds is a unit area on the spherical surface of the integrating sphere, and r is a radius of the integrating sphere, and if the integrating sphere is a uniform diffuse light, then the above mentioned light intensity I becomes a constant.

Also, the incident light is irradiated onto the display panel from a diagonal direction with incident angle θ_i, so the light intensity irradiated on the display panel is attenuated for sin θ_i.

dL=I(θ_i, φ_i)·sin θ_i·ds/r² (1)

As shown in FIG. 20, the unit area ds is given by
ds=(r·sin θ_i·dφ_i)·r·dφ_i (2)

Therefore, if the formula (2) is substituted for formula (1), and the light intensity dL is integrated in the range of incident angle θ_i, 0-π/2, and azimuth angle φ_i, 0-2π, then the incident light intensity L of the display panel is given as follows. $\begin{matrix} L = \int_{0}^{θ_{i} = \frac{π}{2}} \int_{0}^{ϕ_{i} = 2 π} I (θ_{i}, ϕ_{i}) \sin θ_{i} \cos θ_{i} ⅆ θ_{i} & (3) \end{matrix}$

Therefore the light intensity f (θ_i), which enters from the polar θ_idirection, is given by the function in the integration in formula (3), and is given as follows.
f(θ_i)=I(θ_i, φ_I)sin θ_icos θ_i (4)

Sin θ_iin the formula (4) results from the area of the diffuse light source of the integrating sphere for each unit incident angle θ_i, and this means that the light source area of the incident light from just above the display panel (incident angle θ_i=0) is small (sin θ_i=0), and the light source area of the incident light from the lateral direction of the display panel (incident angle θ_i=π/2) is wide (sin θ_i=1). The cos θ_iin the formula (4) is an attenuation component due to the incident angle, and this means that the attenuation of the incident light from just above the display panel (incident angle θ_i=0) is very little (cos θ_i=1), and the attenuation of the incident light from the lateral direction of the display panel (incident angle θ_i=π/2) is large ((cos θ_i=0).

FIG. 21 is a diagram depicting the case when light enters the reflection type display device and is reflected. In the case of the reflection type liquid crystal device shown in FIG. 2, the refractive index n of the glass substrate at the display side and the liquid crystal layer are roughly 1.5, so as FIG. 21 shows, in the structure it is assumed that the reflector 60 comprising a substrate having the reflection electrode shown in FIG. 21 is covered with the medium 61 with the refractive index n comprised of a liquid crystal layer and a substrate at the display side, which are formed thereon. Then the incident light which enters the air layer at incident angle θ_ihas incident angle θ_i′, in the medium 61, is reflected by the reflector 60 at the reflection angle θ_o′ in the medium 61, and is emitted to the air layer at the reflection angle θ_o.

When the light enters from the air layer to the medium 61, a part of the light becomes reflected light R, and does not enter into the medium, so considering this, the intensity f (θ_i′) of the light which enters the reflector 61 at the incident angle θ_i′ can be given as follows. $\begin{matrix} \begin{matrix} f (θ_{i}^{'}) = [1 - R (θ_{i})] \cdot f (θ_{i}) \\ = [1 - R (θ_{i})] \cdot I (θ_{i}, ϕ_{i}) \sin θ_{i} \cos θ_{i} \end{matrix} & (5) \end{matrix}$

Here, R (θ_i) is the reflectance of the light which reflects at the interface of the above mentioned air layer and the medium 61 with the refractive index n. And the following relationship is established between the incident angle θ_iin the air layer and the incident angle θ_i′ in the medium 61.
sin θ_i=n sin θ_i′ (6)

Here, the refractive index of the air layer is 1, and the refractive index of the glass and liquid crystal is n. θ_iis an incident angle in the air layer, and θ_i′ is an incident angle in the liquid crystal layer.

FIG. 22 is a diagram depicting the relationship between the intensity of light f (θ_i′) to enter the reflector 61 and the incident angle θ_i′, calculated by substituting the formula (6) for the formula (5). Here the light intensity was calculated as I (θ_i, φ_i)=1. As FIG. 22 shows, if a uniform diffuse light from an integrating sphere is assumed, the intensity of the incident light to the reflector 60 increases as the incident angle from the incident angle θ_i′=0 increases, the intensity of the incident light becomes the maximum in a certain range of the incident angle θ_i′, and the incident light intensity attenuates considerably at around the incident angle 45°. In other words, an incident angle θ_i′, at which the incident light intensity becomes maximum, exists, and the incident angle differs depending on the refractive index n of the medium.

FIG. 23 is a diagram depicting the relationship between the incident angle θ_i′, when the incident light intensity in FIG. 22 becomes the maximum, and the refractive index n of the medium. As FIG. 23 shows, as the refractive index n of the liquid crystal increases, the incident angle θ_i′, when the incident light intensity becomes the maximum, decreases. Since the typical refractive index of a liquid crystal is about 1.4-1.8, the incident angle θ_i′, when the incident light intensity becomes the maximum, is about 30-38°.

Next we will examine an incident light having the incident light intensity distribution shown in FIG. 22, which reflects on the inclined faces of the undulation of the reflector 61. FIG. 24 is a diagram depicting the relationship between the incident angle, reflection angle and inclination angle with respect to the inclined face of a reflection bump. The incident light and reflected light are symmetrical with respect to a line perpendicular to the inclined face, and a local incident angle α on the micro-mirror face is equal to a local reflection angle β, so the inclination angle ξ, incident angle θ_i′, and reflection angle θ_o′, have the following relationship.

2ξ=θ_i′+θ_o′ (7)

Generally a display is often observed in a direction perpendicular to the display panel. So when light which enters the reflector having undulation at the incident angle θ_i′ is reflected in the 0° direction, the formula (7) becomes ξ=θ_i′/2. In other words, light can be reflected in a direction perpendicular to the display panel when the inclination angle ξ is ½ of the incident angle θ_i′.

As FIG. 22 shows, the distribution of the incident light which enters the bump faces of the reflector with respect to the diffuse light of the integrating sphere has a peak in incident angle area 0-45°. Therefore it is preferable to set the distribution of the inclined faces of the undulation faces of the reflector to a distribution corresponding to the light intensity distribution in FIG. 22. In other words, it is preferable that the existence probability of the inclination angles corresponding to the incident angles at which light intensity is high is increased, and the existence probability of the inclination angles corresponding to the incident angles at which light intensity is low is decreased, so that the over all reflected light intensity is increased.

FIG. 25 is a diagram depicting the distribution of existence probability of the inclination angle corresponding to the incident light intensity distribution in FIG. 22. The example in FIG. 25 shows the case when the refractive index n=1.5 in FIG. 22, and is standardized so that the total sum of the probability becomes 1. The abscissa indicates the inclination angle ξ of the reflection bump face, and the ordinate indicates the existence probability (%). Here, the reflectance of a sample which has the existence probability distribution of the inclination angle shown in FIG. 25 when the inclination angle at which the existence probability is the maximum is determined. FIG. 26 shows the simulation result of such refraction characteristics. Specifically, the inclination angle at which the existence probability is at the maximum is changed by changing the width W of the distribution shown in FIG. 25, and reflectance Y at this time was computed.

As FIG. 26 shows, the range of the inclination angle ξ (=θ_i′/2) at which the existence probability is the maximum is the range where the reflectance is the highest in the area of ξ=about 15-19° (θ_i′=about 30-38°). In other words, in order to increase over all reflectance, it is preferable to maximize the existence probability of the inclination angle ξ=15-19°, at which the incident light with incident angle θ_i′=30-38°, where the incident light intensity shown in FIG. 22 has a peak value, and can be reflected in a direction perpendicular to the display panel.

As described above, in order to reflect light effectively under the uniform diffused light of the integrating sphere, it is theoretically clear that the inclination angle by the undulation for reflection must have the maximum existence probability in about a 15-19° range.

FIG. 27 is a diagram depicting the result of measuring the reflectance with respect to the uniform diffused light of an integrating sphere using an actual prototype sample. In the prototyped reflector, the relationship between the inclination angle ξ_pwhen the existence probability is at the maximum and the measured reflectance is shown.

FIG. 28 shows cross-sectional views depicting a method of forming the reflector prototype. As FIG. 28A shows, resist (LC-200 made by Shipley) 63 is spin-coated on the glass substrate 62 for 20 seconds at 1000-2000 rpm. After pre-baking for 30 minutes at 90° C., UV exposure is performed using the mask 64, as shown in FIG. 28B. Then using a developer (MF 319 made by Shipley), development is performed so as to form the convex parts on the glass substrate, as shown in FIG. 28C. Then as FIG. 28D shows, post-bake is executed for 60 minutes at 120-200° C. so as to round the convex parts. Then an aluminum layer 65 is deposited for 200 nm, as shown in FIG. 28E, so as to fabricate the reflector.

A liquid crystal layer was formed between the reflector and the glass substrate formed as above, and the reflection type liquid crystal display device, as shown in FIG. 28F, is fabricated. Here liquid crystal material MJ 961213 made by Merck was used for the liquid crystal layer, and the thickness thereof was controlled by a spacer with a 3.5 μm diameter. Then the reflectance when a diffused light is entered using an integrating sphere into the reflection type liquid crystal display device prototype fabricated like this was measured. Also the inclination angle distribution of the undulation of the reflector of the prototype and the inclination angle ξ_pat which the existence probability becomes the maximum was determined. FIG. 27 shows the result.

According to this experiment result, a maximum reflectance is obtained when the inclination angle ξ_pat which the existence probability is the maximum is set to around 16-19°. This experiment result roughly supports the simulation result shown in FIG. 26. Compared with the case of the 10° inclination angle, which has been regarded as the optimum value, the sample which the ξ_pinclination angle, at which the existence probability is at the maximum, is around 16-19° has the higher reflectance.

FIG. 29 shows diagrams depicting examples of the pattern of the mask 64 for forming undulation of the reflector. FIG. 29A is an example when the patterns of circles which sizes are different coexist, and FIG. 29B is an example when polygons, such as a triangle, square, hexagon and octagon, coexist. The present invention, however, is not limited to these patterns.

As another example of forming undulation for reflection, a process, where the distribution of thermal deformation characteristics is formed by irradiating UV as shown in FIGS. 3-6 and micro-grooves are formed by final baking thereafter, can be used. The bump shape of the micro-grooves can be controlled by the above mentioned process conditions, so the bump shape is controlled so that the inclination angle ξ_pat which the existence probability is the maximum becomes around 15-19°.

In the present embodiment, the inclination angles of the undulation of the reflector distribute in at least a 0°-25° range, and the existence probability is the maximum at around 15-19°, so a reflection liquid crystal display device having higher reflectance in various environments can be provided.

[Control of Inclination Angle Distribution of Reflector (2)]

FIG. 30 is a diagram depicting the distribution of the inclination angles of the undulation of the reflector to obtain high reflectance with respect to the diffused light of the above mentioned integrating sphere. The abscissa indicates the inclination angle ξ, and the ordinate indicates the existence probability thereof. As described above, it is preferable that the existence probability of the inclination angles be a distribution such that the incident light of the incident angle, at which the incident intensity to the reflector is high, is reflected more in a direction perpendicular to the display panel. FIG. 30 shows a distribution where the existence probability of inclination angles around +15-19° and inclination angles around −15-19° is at the maximum. The + side and the − side exist because when the inclination angle is viewed from a predetermined direction of the display panel, the inclination angle of the incident light from one direction is shown at the + side, and the inclination angle of the incident light from the opposite direction is shown at the − side. Therefore if the distribution diagram in FIG. 30 is folded with the inclination angle 0° as the center, the inclination angle distribution becomes as shown in FIG. 25.

A liquid crystal display is often used as a display panel of a notebook personal computer. FIG. 31 is a diagram depicting a state when the reflection type liquid crystal display device is mounted as the monitor of a notebook personal computer. As FIG. 31 shows, the reflection type liquid crystal display device 70 is often used in a state where angle α is inclined from the horizontal direction. In this case, the display device 70 is a plane perpendicular to the paper face, as shown in FIG. 31. The directions of the X, Y and Z axes are defined as illustrated here.

Considering incident light to the display device 70, the incident angle θ_idistribution along the XY plane of the coordinate is θ_i=−90−90°, since nothing blocks incident light. The incident angle distribution along the XZ plane of the coordinate, on the other hand, is not always θ_i=−90−90°, since incident light is blocked by the keyboard part. In other words, the incident angle range differs between the highest position 70A and the lowest position 70B of the display device 70. The highest position 70A has the widest incident angle range, θ_i=−90−α+β°, and the lowest position 70B has the narrowest incident angle range, θ_i=−90−α°.

Therefore, in the incident lights in the XZ plane direction along the direction perpendicular to the display panel, almost no light enters from the incident angle α−90° (or α+β°−90°). Therefore for the inclination angle of the micro-mirror faces arranged in the XZ plane direction of the display panel, incident angles for reflecting the incident light, which enters from this angle range, to the normal line (0°) direction of the display panel, are unnecessary.

For example, if the inclination of the display panel is α=30° and the refractive index of the liquid crystal layer and the glass substrate is n_LC=1.5, then the inclination angle for reflecting light which enters at 30-90° to the 0° normal line direction is 10-21°, according to the above formulas (6) and (7). In other words, an inclination angle in a 10-21° range is unnecessary for the inclination distribution of undulation in a direction perpendicular to the display panel (XZ plane direction).

Therefore it is desirable that the distribution of the inclination angles in the XY plane direction and the XZ plane direction are as shown in FIG. 32. In other words, the inclination angle distribution in the XY plane direction is the same as the distribution shown in FIG. 30, and for the inclination angle distribution in the XZ plane direction, the − side is the same as in FIG. 30, and the + side is distribution which does not exist in a 10-21° range. FIG. 33 shows the distribution when the distribution in FIG. 32 is folded with the inclination angle 0° as the center.

FIG. 33 shows the inclination angle distribution formed by the undulation of the reflector, including the distribution in the inclined face in the XY plane direction, and distribution in the inclined face in the XZ plane direction. As FIG. 33 shows, when a notebook personal computer is tilted and used, it is preferable that the distribution of the inclined face in the horizontal direction in the display panel is set such that the existence probability is the maximum in a 15-19° inclination angle range, and the distribution of the inclined face in the vertical direction in the display panel is set such that the existence probability has a peak in an 8-10° inclination angle range, and in a 15-19° inclination angle range. In this way, if the angle distribution of the inclined face by reflection undulation is set such that one direction has one peak of existence probability and another direction has two peaks of existence probability according to the direction of the display panel, maximum reflectance can be implemented, even if the display panel is used in an environment which has anisotropy in the incident light direction.

The present inventors manufactured a reflector prototype with the above mentioned inclined face distribution, and confirmed the reflectance thereof. FIG. 34 shows cross-sectional views depicting a method of forming this reflector sample. As FIG. 34A shows, resist (e.g. LC-200 made by Shipley) 63 is spin-coated on the glass substrate 62 for 20 seconds at 1000 rpm. After pre-baking for 20 minutes at 90°, UV exposure is performed using the mask 64, as shown in FIG. 34B. Then using a developer (e.g. MF 319 made by Shipley), development is performed, and convex parts are formed by resist on the glass substrate, as shown in FIG. 34C. The processes in FIGS. 34A-34C are repeated four times by sequentially using the mask patterns (a)-(d) shown in FIG. 35, so as to form convex parts which inclination angles are different, as shown in FIG. 34D. Then as FIG. 34E shows, a post-bake is performed for 80 minutes at 200° C. so as to round the convex parts. Then aluminum 66 is deposited for 200 nm, as shown in FIG. 34F, so as to fabricate the reflector.

FIG. 36 shows a plane shape and cross-sectional shape depicting an example of the convex part of the reflector formed as above. The plane shape of the convex part 67 has different inclined faces in the vertical direction V of the substrate 62, and has the same inclined faces in the horizontal direction H of the substrate 62. In the plan view shown in FIG. 36, contour lines are shown in the convex part 67 so as to show the shape of the inclined face thereof. Since the convex part is rounded by the post-bake, the inclination angle distribution is in about a 0-20° range. And in the vertical direction V of the substrate, inclined faces (ξ1>ξ2) are different, so there are two areas where the existence probability is at a peak, as shown in FIG. 33, and in the horizontal direction H of the substrate, the inclined face (ξ1) is symmetrical, so there is one area where the existence probability is at a peak, as shown in FIG. 33.

By changing the direction of the undulation for reflection between the horizontal direction and the vertical direction as above, the distribution of the inclination angle in the horizontal direction and the distribution of the inclination angle in the vertical direction can be different. As FIG. 36 shows, the distribution of the inclination angles in the horizontal direction and the inclination angles in the vertical direction can be different from each other by combining a semi-circular shape and semi-elliptical shape, as shown in FIG. 36.

The present inventors measured the shape using a non-contact three-dimensional shaped measurement device, nh-3, made by Hishiko, and determined the inclination distribution of the reflector prototype. FIG. 37 shows the measurement result of the inclination angle distribution of the reflector prototype. As FIG. 37 shows, the reflector prototype has the maximum existence probability at absolute values 8° and 18°. For comparison, FIG. 37 also shows the inclination angle distribution of a reflector which maximum existence probability is at 0° and 10°, and also shows the inclination angle distribution of prior art 1 and prior art 2 respectively.

FIG. 38 is a rough cross-sectional view of the reflection type liquid crystal display device created using the above mentioned reflector prototype. The liquid crystal layer (e.g. liquid crystal material MJ 961213 made by Merck) is injected between the reflector and the glass substrate while controlling the thickness with a 3.5 μm diameter spacer. The reflection type liquid crystal display device is secured in a state inclining 30° with respect to a vertical direction, uniform diffused light of the integrating sphere is irradiated, and reflectance was measured using a luminance meter (e.g. BM-5 made by Topcon). FIG. 39 shows the measurement result of the reflectance thereof. As FIG. 39 shows, if the reflector of the present invention is used, reflectance is 61%, where the reflectance improved 10-25% compared with 31% and 53% of the prior arts 1 and 2.

FIG. 33 shows the ideal inclination angle distribution where the refractive index n of the liquid crystal layer and the glass substrate is 1.5, and the angle with respect to the horizontal line of the reflection type liquid crystal display device (inclination angle α shown in FIG. 31) is α=30°. When the refractive index n_LCof the liquid crystal layer and the inclination angle α of the reflection liquid crystal display device are changed, the inclination angle range when the existence probability is at the maximum in the ideal undulation for reflection was examined respectively.

FIG. 40 is a diagram depicting the inclination angle α of a reflection type liquid crystal display device, and the inclination angle range when the existence probability becomes the maximum with respect to the refractive index of the liquid crystal layer. Since the refractive index n_LCof a typical liquid crystal material is 1.4-1.8, the refractive index n_LCwas changed in a 1.4-1.8 range. In a general use case, the inclination a tends to increase as the size of the reflection type liquid crystal display device size decreases, and the inclination a of the display panel is changed in a 0-45° range.

When the inclination angle α of the display panel is 30°, as shown in FIGS. 32 and 33, it is desirable that the existence probability of the inclination angle of the undulation becomes the maximum in a 15-19° range on one hand, and the existence probability of the inclinations angles of the undulation becomes the maximum in two ranges, 8-10° and 15-19° on the other hand. In the case when the inclination angle α of the display panel is 0°, that is the case when the display panel is set vertically, for the inclination angle ξ of the display panel in the vertical direction, the existence probability of the inclination angles of the undulation is the maximum in a 15-19° range, since mainly the incident light from above is reflected in the vertical direction. And there is little incident light coming from the bottom, so an inclined face inclining downward is unnecessary. In the case when the inclination angle α of the display panel is 90°, that is the case when the display panel is set horizontally, it is preferable that the existence probability of the inclination angles of the undulation is at the maximum in a 15-19° range, although this is not shown in FIG. 40. The case when the display panel is horizontal is the same as the distribution example shown in FIG. 30.

As FIG. 40 shows, when the inclination angle α of the display panel is in a 0-45° range, the reflectance can be at the maximum if one inclination angle where the existence probability in the undulation for reflection is at the maximum is 0-16°, and the other inclination angle is in a 14-19° range. As the refractive index n_LCis smaller, the inclination angle to be at the maximum tends to increase.

For a notebook personal computer, the inclination of the display panel differs depending on the user. So it is desirable to form a plurality of areas, where the existence probability of the inclination angle of the undulation for reflection is at the maximum, in the pixel area, so that the maximum reflectance can be implemented at a plurality of inclinations. For example, as FIG. 40 shows, a first combination of 8-10° and 15-19° and a second combination of 10-12° and 15-19° coexist in the same pixel area, as an inclination angle area where the existence probability is at the maximum, which was determined corresponding to cases when the inclination angle α of the display device is 30° and 40°. Or three combined areas determined corresponding to cases when the inclination angle α of the display device is 30°, 35° and 40°, and which coexist. Or three convex patterns coexist. By this, a relatively large reflectance can be implemented even if the inclination angle of display panels are somewhat different.

Using a reflection electrode having the above mentioned inclination angle distribution of undulation for reflection for a pixel electrode, the reflection type liquid crystal display device with the structure shown in FIG. 2 is formed, and a desired display can be implemented by applying a predetermined electric field from the pixel electrode and the transparent electrode of the display side to the liquid crystal layer 34, so as to provide a double defraction function to the liquid crystal layer 34. In other words, the liquid crystal layer 34 is driven in field effect double defraction mode. Also, a guest-host type liquid crystal display device can be implemented by including dye into the liquid crystal layer 34.

[Example of Undulation for Reflection Where Different Directivities Coexist]

Japanese Patent Laid-Open No. H11-295750 discloses a reflection type liquid crystal display device which uses a pixel electrode as a reflection electrode. According to this disclosure, the pixel electrode is divided into two areas, bump shapes having reflection characteristics with strong directivity are formed in one area, and bump shapes having reflection characteristics with strong diffusibility are formed in the other area.

However, in the case of a higher precision liquid crystal display device, the pixel area becomes smaller, and it is probably difficult to form different bump shapes respectively for the pixel areas divided into two, as seen in the prior art.

Therefore in the present invention, bump shapes having reflectance characteristics with strong directivity and bump shapes having reflection characteristics with strong diffusibility coexist in a pixel area. FIG. 41 is a cross-sectional view depicting two reflection bump shapes coexisting in such a pixel area. Bump A has a gentle inclined face with a thin film thickness, where the top face is relatively flat, so reflected light is directed to the vertical direction. And bump B, on the other hand, has a sharp inclined face with thick film thickness, the top face protrudes, so reflected light diffuses widely.

FIG. 42 is a plan view of the pixel area PX in the present embodiment. As illustrated, bump A and bump B, shown in FIG. 41, coexist in the pixel area PX.

FIG. 43 shows cross-sectional views depicting the manufacturing process for forming the undulation for reflection in FIG. 42. At first, as FIG. 43A shows, resist (e.g. LC-200 made by Shipley), which is a photo-sensitive resin, is spin-coated for 20 seconds at 2000 rpm on the glass substrate 62. After pre-bake is performed for 20 minutes at 90° C., UV exposure is performed using the mask 64A shown in FIG. 43B. Then using a developer (e.g. MF 319 made by Shipley), development is performed so as to form the convex part corresponding to bump A on the glass substrate 62, as shown in FIG. 43C. Then, as FIG. 43D shows, a post-bake is executed for 80 minutes at 200° C., so as to round the convex part to form bump A.

Then as FIG. 43E shows, the resist is spin-coated for 20 seconds at 1000 rpm. By this, a resist layer thicker than the above mentioned resist can be formed. After pre-baking for 20 minutes at 90° C., UV exposure is performed using the mask 64B, as shown in FIG. 43F. Then development is performed using the above mentioned developer, and a convex part corresponding to bump B is formed on the glass substrate, as shown in FIG. 43G. Then a post-bake is performed for 80 minutes at 200° C., as shown in FIG. 43H to round the convex part, and bump B is formed. Since this post bake is performed at a temperature lower than that for forming bump A, sagging of the thick resist film by heating is less, and bump B with stronger diffusibilty can be formed.

Then as FIG. 43I shows, the reflector (pixel electrode) is fabricated by depositing aluminum 64 for 200 nm. As mentioned above, the roundness of the undulation can be changed by changing the resist film thickness and the post-bake temperature between bump A and bump B, and a reflection face, where undulation with different directivity during scattering coexist, can be created.

As mentioned above, it is preferable that the reflector of the reflection type liquid crystal display device reflect incident light from various directions to a direction perpendicular to the display face. Therefore, when the resist layer is patterned and rounded by baking to form the inclined face, it is preferable that the inclined face direct 360°. Therefore a circular pattern has been proposed as a pattern of the resist film. Examples are disclosed in Japanese Patent Laid-Open No. H11-337935, Japanese Patent Laid-Open No. H11-337964, and Japanese Patent Laid-Open No. H5-281533. These patents proposed forming the circular patterns at random so as to prevent the formation of moiré patterns by the interference of reflected light, or forming doughnut patterns with a large radius and small circular patterns with a small radius at random, so as to improve the reflection characteristics.

Japanese Patent Laid-Open No. H5-281533 discloses forming coexisting large circular patterns and small circular patterns at random. An example is shown in FIG. 44. However, if large circular patterns with a large radius are arranged at random, adjacent resist patterns unite by sagging in a cross-sectional shape by heating during the post-baking process after exposure and development. The shaded circular patterns shown in FIG. 44 show the state when the patterns are too close to each other, and which unite during baking.

So in the present embodiment, as FIG. 45 shows, the circular patterns with a large radius and circular patterns with a small radius coexist in the resist pattern, and are arranged such that the distance between a large circular pattern and a small circular pattern is always smaller than the distance between large circular patterns. In other words, a large circular pattern coming too close to another large circular pattern is prevented. If possible, small circular patterns are arranged around a large circular pattern, so that large circular patterns do not come close to each other. By this, the density of an inclined face can be increased, and areas where patterns are united during baking can be decreased.

FIG. 46 shows diagrams depicting the resist pattern of the present embodiment.

FIG. 46A is an example when relatively large circular patterns are arranged. Four large circular patterns P1 are arranged in the pixel area PX. The resist pattern must have a certain size. If the pattern is too small, the inclination angle will be insufficient because of sagging in the cross-sectional shape during post-bake. In the case of the pattern in FIG. 46A, however, reflectance cannot be increased since the density of the inclined face to be formed is low.

As FIG. 46B shows, it is possible to increase the density of the large circular patterns P1. However, if the large circular patterns P1 come too close to each other, the edges of the circular patterns may unite, as shown by shading, because of sagging by heat during post-bake. Such a uniting decreases the area of the inclined face to be designed, which is not desirable.

As in the present embodiment, the density of the relatively large circular patterns P1 is not dense, as shown in FIG. 46A, and the distance L1 between the patterns P1 is maintained to be relatively large, and the relatively small circular patterns P2 are arranged in the space between the large circular patterns P1, so as to increase the density of the inclined faces, as described referring to FIG. 45 and as shown in FIG. 46C. By this, the relatively large circular patterns do not unite with each other, and even if they do unite, this is limited to the space between a large circular pattern P1 and a small circular pattern P2 (shaded area in FIG. 46C). Such a united area is relatively small compared with the united area between the large circular patterns P1, and the decrease of the inclined face area can be minimized.

As FIG. 46C shows, the distance L1 between the large circular patterns P1 is long enough not to cause uniting, and the small circular patterns P2 are arranged in the areas between the circular patterns P1. As a result, the distance L2 between the large circular pattern P1 and the small circular pattern P2, which is closest to P1, is always shorter than the distance L1 between the large circular pattern P1 and the large circular pattern L1 closest thereto.

FIG. 47 is a diagram depicting another resist pattern. The above example uses circular patterns so that the inclined face of the undulation for reflection turn in 360° directions, but a polygon, which sides direct a plurality of directions, preferably three or more, instead of a circle, can implement a similar high reflectance.

FIG. 47 is an example of a pattern of resist where many hexagons are arranged close to each other so that adjacent sides are parallel to each other in the pixel area PX. At the edge of the pixel area PX, an entire hexagon cannot fit, and trapezoids and pentagons are arranged, but basically hexagons are arranged like tiles in this resist pattern. By arranging each side to be in parallel, uniting during post-bake can be prevented even if a hexagon comes very close to another.

Using such a mask pattern, the resist layer is exposed and developed, and post-bake is executed, then the cross-sectional shape sags due to heat, and undulation for reflection, which has an inclined face inclined in at least three directions, can be formed.

FIG. 48 is a diagram depicting another resist pattern. In the example in FIG. 48, not hexagons but a plurality of equilateral triangles are arranged such that each side comes close to another in parallel. In this case as well, the resist layer is exposed and developed, and post-bake is executed, then the cross-sectional shape sags due to heat, and undulation for reflection, which has inclined faces inclining in at least three directions, can be formed. The present embodiment can form the undulation for reflection having inclined faces at high density even if another polygon shape is used.

The process of forming the undulation for reflection using the patterns in FIGS. 45, 47 and 48 is the same as the process shown in FIG. 28. For the mask 64 in the exposure process of the resist layer, the patterns in FIGS. 45, 47 and 48 are used. By this, high density inclined face distribution can be formed without allowing to patterns unite with each other, and the reflectance of the reflector can be increased.

[Embodiment of Guest-Host Liquid Crystal Layer]

The rough configuration of the reflection liquid crystal display device of the present embodiment is the same as FIG. 2. In this embodiment, however, a guest-host liquid crystal layer where dichroic dye are mixed in the liquid crystal is used.

[Forming Undulation by Half Exposure]

The main point of the present embodiment is that in order to control undulation shapes on the surface of the reflection layer, the reflection layer is configured such that the reflected light scattering width in the incident plane when parallel light enters depends on the azimuth of incident light, by forming a light absorption layer which light absorption characteristics depend on the azimuth in the front face of the reflection layer, and bump shapes on the surface of the reflection layer are controlled by adjusting such that the azimuth, when the reflection light scattering width is at the maximum, and the azimuth when the light absorption of the light absorption layer is at the maximum or at the minimum, roughly match.

CONCRETE CONFIGURATION

As FIG. 83 shows, we fabricated diffuse reflectors comprised of (a) a circular pattern, (b) an elliptical pattern, (c) a trapezoidal pattern, (d) a cocoon-shaped pattern, and (e) a wrinkle pattern.

The circular, elliptical, trapezoidal and cocoon-shaped patterns were fabricated as follows. Resist AFP 750 (made by Shipley) was coated on a 0.7 mm thick glass substrate to be 3 μm, then using a mask pattern where circular, elliptical, trapezoidal or cocoon-shaped patterns are arranged at random, half exposure was performed at a 80 mJ/cm²exposure energy. After the half exposure and development, bake is performed for 40 minutes at 135° C., so that each pattern is smoothed by heat and inclination is controlled. Then bake is performed for 1 hour at 200° C. to completely cure the resist, and the reflector was fabricated by vacuum deposition of Al on the resist to be about a 200 nm thickness.

For the wrinkle patterns of the micro-grooves, resist AFP 750 was coated on the 0.7 mm thick glass substrate to be 3 μm, and UV with a 3900 mJ/cm²exposure energy was irradiated. After UV irradiation, bake was performed for 90 minutes at 135° C. to generate fine wrinkles on the resist surface. Then final bake was performed for 1 hour at 200° C., and the reflector was fabricated by vacuum deposition of Al on the resist to be about a 200 nm thickness.

To generate more wrinkle patterns in a predetermined direction, a rectangular transparent electrode made of indium tin oxide (ITO) was formed on the glass substrate.

By using this pattern, more wrinkles are generated in a direction parallel with the sides of the ITO rectangle (azimuth: 0-180° and 90-270°).

Parallel lights are entered into these reflectors changing incident angles, and the reflection characteristics in a 0° direction were measured.

FIG. 84 shows the result of measuring the reflection characteristics. This shows the reflectance on the ordinate when the polar angle of the incident light (incident angle on the abscissa) and the azimuth angle are changed.

As FIG. 84 shows, the reflection characteristics do not depend on azimuth (shown in rectangular) in the case of a circular pattern, but in the case of an elliptical, trapezoidal, cocoon-shape and wrinkle patterns, the reflection characteristics change considerably depending on the azimuth. In other words, in the case of elliptical, trapezoidal and cocoon-shaped patterns, the scattering width is wider in the minor axis direction than the major axis direction, and in the case of a wrinkle pattern, the scattering width in a direction parallel with the sides of the ITO rectangle is wider than that of other directions. Therefore it is preferable to select an optimum pattern according to the intended use of the liquid crystal display panel.

Dichroic dye MA 981103 (made by Mitsubishi Chemical) was mixed into the n-type liquid crystal MJ 95785 (made by Merck), the density of the dye was changed to obtain contrast 5, and the relationship between the twist angle and the reflectance of the liquid crystal layer was examined.

FIG. 85 shows the result.

As FIG. 85 shows, a brighter reflectance is obtained as the cell thickness decreases, and a maximum reflectance is obtained at a 180° twist or 330° twist. However, if a 330° twist is implemented, the voltage reflectance characteristics has hysteresis, so generally the twist angle must be 240° or less. So we examined the viewing angle characteristics of the bright state and the dark state of the reflection guest-host liquid crystal when the cell thickness of the guest-host liquid crystal is 3 μm, and a 180° twist structure was created by performing parallel rubbing processing in the azimuth 0° of the top and bottom substrates.

FIG. 86 shows the result.

In the bright state, the reflection characteristics do not change between the azimuth 0° direction and the azimuth 90° direction, so the reflection characteristics do not depend on the azimuth, but in the dark state, the characteristics differ considerably between the azimuth 0° direction and the azimuth 90° direction. In other words, the light absorption characteristics depend on the azimuth in the dark state, where absorption in the larger incident angles is higher in the azimuth 0° direction than in the azimuth 90° direction.

In the case of an elliptical pattern, for example, fabricated in the fabrication example 1, the reflection characteristics depend on the azimuth angle.

Here a guest-host liquid crystal, which is twisted 180°, is considered, as FIG. 87 shows. When the intensity of light, which enters at incident angle θ and azimuth angle φ is IO (θ, φ), the guest-host layer transmittance of light which enters at incident angle θ and azimuth angle φ is T (θ, φ), and the reflectance of the reflector when the light at incident angle θ and azimuth angle φ reflects in the 0° direction is R (θ, φ). The light intensity I (θ, φ) when the light enters the reflection guest-host liquid crystal at incident angle θ and azimuth angle φ and is reflected in the 0° direction is given by the following formula.
I(θ, φ)=I₀(θ, φ)·T(θ, φ)·R(θ, φ)·T(θ=0°, φ=0°) (11)

Since light enters from various directions in an environment where a reflection type liquid crystal display device is used, it is necessary to assume that light which enters at incident angle θ actually enters from all azimuths. When light at incident angle θ enters from all azimuths, formula 1 is integrated for all azimuths, but an approximate light value can be given by an average value of the azimuth φ and an azimuth perpendicular thereto, φ+90°. (To obtain a more accurate value, increase the number of azimuths and average the values).

In the case of an elliptical pattern, for example, azimuth 0° and 180°, and 90° and 270° are almost the same, so light from all azimuths can be approximated by the sum of the azimuth 0° direction and the azimuth 90° direction, as shown in the formula (12).
I(θ, φ)≈(½)I₀(θ, φ=0°)·T(θ=0°, φ=0°)·[T(θ=0°, φ=0°)·R(θ, φ=0°)+T(θ, φ=90°)·R(θ, φ=90°) (12)

So we estimated the reflectance based on the formula (12) for the case when a diffuse reflector with an elliptical pattern and a guest-host liquid crystal are combined. Table 4 shows the result when the reflectance was calculated by the formula (12) for the case when the major axis of the ellipse and the rubbing direction are the same (case 1), the case when the minor axis of the ellipse and the rubbing direction are the same (case 2), and the case when a circular reflector is used (case 3). Reflectance and contrast were calculated in Table 4. As Table 4 shows, contrast is higher in the elliptical pattern than in the circular pattern, and especially under the conditions of case 2, contrast increased considerably.

TABLE 4

Reflectance estimation result
	Bright state	Dark state	Contrast
	θ = 30°	45°	60°	θ = 30°	45°	60°	θ = 30°	45°	60°

Case 1	74.7%	32.9%	3.6%	16.2%	5.9%	0.9%	4.6	5.6	4.0
Case 2	74.7%	32.9%	3.6%	16.1%	5.3%	0.2%	4.6	6.2	18.0
Case 3	75.2%	32.9%	3.5%	16.4%	8.4%	1.3%	4.6	4.3	2.7

In other words, as FIG. 87 shows, contrast increases considerably by making the minor axis of the ellipse and the rubbing direction the same.

We actually fabricated cells for each case 1-3. Dichroic dye MA 981103 is mixed at 4.3 wt % to liquid crystal MJ 95785, and the amount of mixing chiral material CB-15 (made by Merck) was adjusted so that the chiral pitch becomes 8 μm. The cells were implemented by sealing this guest-host liquid crystal into the cells using a 4 μm diameter spacer.

Considering the environment where a reflection liquid crystal display device is used, the reflection characteristics and the contrast were measured using an integrating sphere. Table 5 shows the result. As Table 5 shows, it was confirmed that contrast becomes higher than the case 3 which is the conventional approach, by structuring an actual cell, as in case 2.

TABLE 5

Integrating sphere measurement result
	Reflectance	Contrast

	Case 1	44.2%	5.3
	Case 2	44.2%	6.2
	Case 3	45.2%	5.1

A similar result was obtained when trapezoidal, cocoon-shaped and wrinkled patterns were used as the bump pattern of a diffusion reflector, and high contrast characteristics were obtained by combining the axis of a guest-host liquid crystal and azimuth of a reflector appropriately.

CONCRETE CONFIGURATION EXAMPLE

FIG. 88 shows the result of measuring the incident light angle characteristics of polarizer G 1220 DU (made by Nitto Denko). The azimuth 0° is the direction of absorption axis of the polarizer, and the azimuth 90° is the direction of the transmission axis.

As FIG. 88 shows, the transmission axis direction (azimuth 90°) has a higher transmittance in a wide angle range than the absorption axis direction (azimuth 0°). So this polarizer is optically contacted to the elliptical pattern, and the reflectance was measured using an integrating sphere.

Table 6 shows the measurement result. Case 1 is when the major axis direction of the elliptical pattern and the absorption axis direction of the polarizer are matched, and case 2 is when the minor axis direction of the elliptical pattern and the transmission axis direction of the polarizer are matched. As Table 6 shows, it was confirmed that case 1 can implement a higher reflectance than case 2.

TABLE 6

Reflection characteristics when polarizer G 1120 DU and
elliptical reflector are combined (integrating sphere)
	Reflectance

	Case 1	38.2%
	Case 2	36.5%

Therefore as FIG. 89 shows, one polarizer type reflection liquid crystal display device was fabricated by layering liquid crystal layer 402 (FT-5045LE (made by Chisso)), λ/4 plate 403, λ/2 plate 404, and polarizer 405 (G1220DU) on the diffuse reflector 401. Table 7 shows the reflectance and the contrast characteristics measured using an integrating sphere.

TABLE 7

Reflectance and contrast of one polarizer type
(integrating sphere)
	Reflectance	Contrast

	Case 1	35.3%	17.5
	Case 2	34.1%	17.1
	Case 3	35.1%	17.2

Here case 1 is when the major axis direction of the elliptical pattern and the absorption axis direction of the polarizer are matched, case 2 is when the minor axis direction of the elliptical pattern and the transmission axis direction of the polarizer are matched, and case 3 is when a circular pattern diffuse reflector is used. As Table 7 shows, compared with case 3 which is prior art, the reflectance increased somewhat in case 1. In other words, in the case of a polarizer type as well, the reflectance improved by combining the axis of the polarizer and the azimuth of the reflector appropriately.

As described, according to the present embodiment, a reflection electrode, which can implement stable high reflectance characteristics, can be formed, and a guest-host type and one polarizer type reflection liquid crystal display devices with high reliability, which allows a display with high lightness, can be implemented.

[Front Light Structure]

The reflection type liquid crystal display device lights the display face by reflecting external light without disposing backlight. Therefore, the reflection type liquid crystal display device has low power consumption and is useful as a display panel of portable information terminals and portable telephones. However, use is limited to a bright place, since external light is used. So a liquid crystal display device with a front light which is turned on only when the unit is in use in a dark place has been proposed.

FIG. 49 is a diagram depicting the configuration of a conventionally proposed reflection type liquid crystal display panel with a front light. As FIG. 49 shows, a front light 70 is installed on the display side of the reflection liquid crystal display panel 73. In the reflection type liquid crystal display panel 73, a liquid crystal layer, which is not illustrated, is inserted between the rear side substrate 73B, having a reflector structure, and the display side substrate 73A. And on the display side substrate 73A, the front light 70 is installed, and the front light 70 is comprised of a light source 71 and a transparent substrate 72 which guides the light from the light source to the entire surface of the display, and scatters the light to the display panel 73 side using the scattering layer or the prism layer formed on the surface. The light of the light source 71 is scattered by the difference of the refractive index between the scattering layer or the prism layer formed on the surface of the transparent substrate 72 and the air layer, and a part of the scattered light is scattered to the display panel 73 side.

However, in the case of the reflection type liquid crystal display device configured as in FIG. 49, the scattering layer or the prism layer is formed on the surface of the transparent substrate 72, and an observer sees characters and images on the display panel 73 via this scattering layer and prism layer. Therefore characters and images are distorted or blurred by the scattering layer or the prism layer, which drops the image quality.

So the present embodiment has a front light structure such that the transparent substrate, which guides light only when the light source is turned on, has a scattering characteristic, and the transparent substrate does not have this scattering characteristic when the light source is not turned on. By using this structure, where the front light structure does not use the scattering function when in normal use using external light, characters and images observed on the display panel are not distorted or blurred. Only in limited cases, such as use in a dark place, the front light structure provides light from the light source via the scattering characteristic, so the display panel is brightened and minimum functions required as the display panel can be secured, even if characters and images are somewhat distorted and blurred.

FIG. 50 shows diagrams depicting a first example of the front light. The front light 70 shown in FIG. 50 comprises a transparent substrate 74, where the surface of a transparent substrate made of acrylic is sand-blasted so as to form a scattering layer 75 on the surface, a transparent substrate 76 made of acrylic, a fluid 77, such as silicon oil to be filled between the substrates, a fluid pump 78 and a fluid tank 79. The front light 70 further comprises a linear light source 71 made of a cold cathode fluorescent tube. Between the substrates 74 and 76, the fluid stored in the fluid tank 79 is filled in or taken out by the fluid pump 78. The refractive index of this fluid 77 is n=1.5, which is roughly the same as the transparent substrates 74 and 76.

As FIG. 50A shows, when the reflection liquid crystal display panel is used in a bright place, the light source 71 is in the off state, and the fluid 77 is filled into the gap between the transparent substrates 74 and 76. By this, an observer cannot see the scattering layer 75 since the refractive index is the same as the fluid 77. Therefore when the liquid crystal display panel is used in a bright place, characters and images on the display panel 73 are not blurred or distorted.

When the reflection liquid crystal display panel is used in a dark place, on the other hand, the light source is in the on state, and the fluid 77 is taken out of the gap between the transparent substrates 74 and 76 by the fluid pump 78, and the air layer is filled into the gap of the substrates, as shown in FIG. 50B. Therefore the refractive index difference is generated between the acrylic of the transparent substrate material (refractive index is about 1.5) and air (refractive index of 1.0) in the scattering layer 75, and the original function of the scattering layer is presented. So lights which have been guided, repeating internal reflection from the light source 71 which is at the end of the transparent substrates 74 and 76, are scattered by this scattering layer 75, and lights the reflection liquid crystal display panel 73. As a result, a bright display panel can be implemented even in a dark place.

When this front light 70 is viewed from the observer side, the scattering layer 75 of the transparent substrate 74 is seen, and the display of the reflection liquid crystal display panel 73 is distorted. However such distortion is equivalent to that of a conventional reflection liquid crystal display panel with a front light.

As described above, the same display as a reflection display panel without a front light is obtained when used in a bright place, and light from the light source can be used for illuminating the reflection liquid crystal display panel when used in a dark place, therefore a bright display is implemented.

FIG. 51 shows diagrams depicting a second example of a reflection liquid crystal display panel with a front light according to the present embodiment. In this example, a transparent electrode (ITO) 81 whose the main component is indium oxide is formed on the surface of two transparent substrates 74 and 76 made of glass, for example, and the liquid crystal layer 80, which state changes depending on the electric field, is sandwiched in the gap between the transparent substrates. Voltage V1 is applied or not applied between the transparent electrodes 81 depending on the switch SW. Normally, this liquid crystal layer 80 becomes a transparent state when voltage V1 is applied between the transparent electrodes, and becomes a scattering state when the voltage between the transparent electrodes is 0. Therefore in a bright place, the switch SW is turned on to make the liquid crystal layer 80 to be transparent, and in a dark place, the switch SW is turned off to make the liquid crystal layer 80 to be a scattering state.

The liquid crystal materials for which the scattering state and transmission state can be switched are (1) a liquid crystal using a dynamic scattering effect, (2) a liquid crystal using a phase transition effect between the cholesteric phase and the nematic phase, and (3) a polymer dispersion type liquid crystal, and one of these liquid crystals can be used.

In the case of the example in FIG. 51, compared with the example in FIG. 50, a transparent substrate with a scattering layer, pump and tank are unnecessary, where the time for filling and taking out fluid can be saved. Also in the case of the polymer dispersion type liquid crystal, the degree of anisotropy of the refractive index of spherical liquid crystals in the polymer can be adjusted by applied voltage. Therefore the degree of scattering of the liquid crystal layer 80 can be adjusted by adjusting the applied voltage, and an observer can adjust the degree of scattering of the lights from the light source 71 to increase the brightness, or the degree of scattering of the lights is decreased to control the distortion of the display screen.

Even in the example of FIG. 51, the display of the reflection type liquid crystal display panel looks as if viewing through frosted glass when the light source 71 is turned on and the liquid crystal layer 80 has the scattering characteristic, but this is equivalent to a conventional reflection type liquid crystal display panel with a front light. And when the light source 71 is off in a bright state, the liquid crystal layer 80 is transparent, and the display is not blurred or distorted. In other words, this example, which is a reflection type liquid crystal display panel with a front light, allows a display quality equivalent to a reflection type liquid crystal display panel without a front light when the front light is not on, and allows a display quality equivalent to a normal reflection type liquid crystal display panel with a front panel when the front light is on.

FIG. 52 shows diagrams depicting a third example of a reflection liquid crystal display panel with a front light. In this example, the transparent electrode 81 is formed on the inner face of the transparent substrates 74 and 76, such as glass, and a prism layer 82 having prism-shaped fine undulation is formed inside the transparent substrate 74. And the liquid crystal layer 80 having refractive index anisotropy is sealed inside the transparent substrates 74 and 76. The molecule alignment direction of the crystal molecules having refractive index anisotropy is changed by the electric field, and the direction of the refractive index anisotropy changes. Here one refractive index of the liquid crystal layer 80, having refractive index anisotropy, is matched with the refractive index of the prism layer 82.

As FIG. 52A shows, when the display panel is used in a bright place, voltage is applied to the liquid crystal layer 80, or no voltage is applied, so that the refractive index of the prism layer 82 and the refractive index of the liquid crystal layer 80 are matched in the direction from the display side to the reflection display panel 73. In this state, the refractive index of the prism layer 82 and the refractive index of the liquid crystal layer 80 match in the direction from the display side to the reflection display panel 73, where a scattering state caused by the prism layer 82 disappears and the front light structure becomes transparent. As a result, the state becomes the same as the state of a reflection type liquid crystal display panel without a front light, where the display screen is not blurred or distorted.

For use in a dark place, on the other hand, no voltage is applied or voltage is applied to the liquid crystal layer 80, so that the refractive index of the prism layer 82 and the refractive index of the liquid crystal layer 80 are different in the direction from the display side to the reflection display panel 73, as shown in FIG. 52B. Because of this, a refractive index difference is generated at the interface between the prism layer 82 and the liquid crystal layer 80, and light from the light source 71 is refracted. This refracted light becomes the illumination light to the reflection type liquid crystal display panel 73, and a bright display can be implemented.

In this example, prism shapes are formed on the surface of the transparent substrate 74, but a similar effect can be expected by forming a scattering layer on the surface of the transparent substrate 74 by a sand-blast process.

By applying this structure, a similar effect as example 2 can be obtained, and a transmission state and scattering state can be switched much faster due to the nature of the liquid crystal layer 80. Also compared with the polymer dispersion type liquid crystal in example 2, voltage can be directly applied to the liquid crystal layer 80, so the applied voltage to the liquid crystal layer 80 can be lower than using the polymer dispersion type liquid crystal. And by matching the refractive index of the liquid crystal layer with the refractive index of the prism layer 82 in a state where voltage is not applied to the liquid crystal layer 80, it is unnecessary to apply voltage to the light source 71 and the transparent electrode 81 when the display panel is used in a bright place, which further decreases power consumption.

FIG. 53 shows diagrams depicting a fourth example of a reflection type liquid crystal display panel with a front light. In this example, the transparent electrode 81A, which is formed on the transparent substrate 74, which is the light guiding plate of the front light 70, is separated into strips, so that applying voltage 81A-1 or not applying voltage 81A-2 can be selected for each strip. And a liquid crystal layer, which state changes depending on whether voltage is applied, is filled between the transparent substrates 74 and 76. FIG. 53A shows a cross-sectional structure, and FIG. 53B shows a plane structure of the separated transparent electrode 81A.

If this structure is used, the area of the liquid crystal layer to be the scattering state can be appropriately changed by changing the number of transparent electrodes 81A to which voltage is applied, and the quantity of illumination light can be adjusted to a certain degree. Therefore in this configuration, the degree of scattering can be adjusted by selecting the transparent electrodes to which voltage is applied, even if a scattering type liquid crystal where the degree of scattering cannot be adjusted, a liquid crystal using a dynamic scattering effect, or a liquid crystal using a phase transition effect between the cholesteric phase and the nematic phase, is used for the liquid crystal layer 80.

If the degree of scattering by the liquid crystal layer of the front light is high, the reflection type liquid crystal display panel with a front light scatters the light from the light source 71 very well, and illuminates the reflection liquid crystal display panel 73 very well, therefore the brightness of the reflection liquid crystal display panel increases. However, the display image clouds and the resolution drops since the scattering layer exists between the observer and the reflection type liquid crystal display panel. Therefore, if a degree of scattering is possible, the observer can adjust it to optimize the display quality for viewing.

FIG. 54 shows diagrams depicting a fifth example of a reflection type liquid crystal display panel with a front light. In the front light 70 of this example, just like the second example shown in FIG. 52, a transparent electrode 81 is formed inside the transparent substrates 74 and 76 and the liquid crystal layer 80 is filled between them. The liquid crystal layer 80 is a polymer dispersion type liquid crystal where refractive index anisotropic resin is used for the polymer, and is configured such that the normal light refractive index and the abnormal light refractive index of the liquid crystal grains 90 match the refractive index of the polymer in two directions in a state where voltage is not applied between the transparent electrodes.

Details of the polymer dispersion type liquid crystal are shown at the right in FIG. 54. While liquid crystal grains 90 having refractive index anisotropy are dispersed in polymer not having refractive index anisotropy in the case of polymer dispersion type liquid crystal A, liquid crystal grains 90 having refractive index anisotropy are dispersed in polymer having refractive index anisotropy in the case of polymer dispersion type liquid crystal B.

It is assumed that in crystal grains 90, molecules are aligned in the thickness direction of the front light 70, the refractive index in the thickness direction of the front light matches with the polymer 92 and the transparent substrates 74 and 76 when voltage is not applied between the transparent electrodes, and these refractive indexes do not match when voltage is applied between the transparent electrodes.

In this case, in the polymer dispersion type liquid crystal A, the refractive index of the liquid crystal grains 90 in the vertical direction match the polymer 92 and the transparent substrates 74 and 76, and lights in the vertical direction do not have a refractive index difference, so no refraction and scattering occur. However, the horizontal refractive index is different between the polymer 92 and the liquid crystal grains 90, so refraction occurs to not only horizontal light but also to diagonal light, that is, to the horizontal direction vector component of the lights. Therefore, when the reflection type liquid crystal display panel 73 is viewed diagonally, the front panel 70 looks clouded, due to this refraction.

If polymer dispersion type liquid crystal B is filled between the transparent substrates 74 and 76, on the other hand, liquid crystal molecules align in the thickness direction of the front light when voltage is not applied between the transparent electrodes, and the direction of the refractive index anisotropy of the liquid crystal grains 90 and the direction of the refractive index anisotropy of the polymer 92 match. Therefore, in this state, a refractive index difference between the liquid crystal grains 90 and the polymer 92 is not generated at all from any direction, and the front light becomes transparent from all directions. Therefore, compared with the case of using polymer dispersion type liquid crystal A, a distortion and fogging of images viewed from a diagonal direction can be prevented when the panel is used in a bright place of FIG. 54A.

When the panel is used in a dark place and voltage is applied between the transparent electrodes as FIG. 54B, the direction of refractive index anisotropy of the liquid crystal grains 90 mismatches with the direction of the refractive index anisotropy of the polymer 92. This is because the direction of the anisotropy of the polymer 92 is not changed by an electric field. Therefore the front light 70 becomes a scattered state, and light from the light source 71 is scattered to the reflection type liquid crystal display panel 73 side, which brightens the liquid crystal display surface. However, the color of the liquid crystal layer 80 becomes cream-yellow, and blurring and distortion occur to the display screen.

In this case, the direction of the refractive index anisotropy of the liquid crystal grains 90 can be adjusted by adjusting the voltage to be applied between the transparent electrodes. In other words, if the applied voltage is increased, the degree of scattering in the liquid crystal layer increases, incident light to the reflection liquid crystal display panel 73 increases, and the screen brightens, but the screen may become too white, making it difficult to view. If the applied voltage is decreased, on the other hand, the degree of scattering in the liquid crystal layer decreases, and the screen darkens, but the transparency of the screen increases. So by adjusting the applied voltage, the degree of brightness of the screen and the degree of contrast can be set as the observer desires.

FIG. 55 is a diagram depicting a sixth example of a reflection type liquid crystal display panel with a front light. In the previous examples in FIGS. 50-54, light from the light source 71 are guided in the two transparent substrates. Whereas in the example in FIG. 55, the light source 71 is disposed on the side face of the substrate 74 at the display face side of the two transparent substrates, and light is guided mainly in the substrate 74 in the display face side. Light is scattered by the prism-shaped undulation 82 arranged on the side face of the reflection type liquid crystal display panel 73 of the substrate 74, so as to illuminate the reflection type liquid crystal display panel 73. On the transparent substrates 74 and 76, a transparent electrode, which is not illustrated, is formed, and the liquid crystal layer 80 is filled between the substrates.

When light is guided in the two transparent substrates 74 and 76 at the top and the bottom, as shown in FIGS. 50-54, light guided from the top and bottom transparent substrates contact the prism-shaped undulation 82. In this case, it is desirable that light from the top transparent substrate 74 is refracted, scattered and transmitted downward, and light from the bottom transparent substrate 76 is reflected, scattered and reflected downward as well. However, more light is actually refracted, scattered and transmitted than light reflected, scattered and reflected downward, so it is difficult to efficiently reflect and scatter light from the bottom substrate.

Whereas in the case of the configuration in FIG. 55, a prism layer 82 is disposed at the display panel 73 side of the transparent substrate 74, where light from the light source is transmitted. Therefore light irradiated to the prism layer 82 is the light transmitted through the top transparent substrate 74, and more light refracted and scattered through the prism layer 82 enters the reflection type liquid crystal display panel 73 side. Therefore the prism-shaped undulation 82 only needs to be refraction scattering shapes, and a simplification of shapes and an improvement of illumination efficiency can be implemented.

When the liquid crystal layer 80 having scattering characteristics is also sealed, more light from above is scattered to the liquid crystal layer 80 and is transmitted downward, and the quantity of light to be reflected and scattered is low. Therefore, in the above structure, illumination efficiency is higher. For light from the light source 71, the quantity of incident light from the light source decreases since only one transparent substrate 74 guides light, but the quantity of incident light from the light source 71 can be improved by increasing the thickness of the transparent substrate 74.

FIG. 56 is a diagram depicting the seventh example of a reflection type liquid crystal display panel with a front light. The configuration of FIG. 56 improves on the structure of FIG. 55. In other words, FIG. 56 shows a structure wherein a transparent light guiding plate 94 which has a light source 71 on the side face, is bonded with a substrate where an element which exhibits scattering characteristics is sealed between the two transparent substrates 74 and 76. Specifically, a prism layer 82 is formed between the transparent substrates 74 and 76 made of glass, and the substrate for scattering, where the liquid crystal layer 80, which refractive index status is changed by an electric field is filled, is bonded with the transparent light guiding plate 94 by optical bonding 96. In the case of this structure, fabrication of the two transparent substrates 74 and 76, where an element which exhibits scattering characteristics is sealed, and fabrication of the light guiding plate with a light source 94, can be separated, so that the fabrication process steps are separated each other and improves yield. The glass substrates 74 and 76 sandwiching the liquid crystal layer 80 are thin, 0.5-0.7 mm for example, and the plate thickness of the transparent light guiding plate 94, where the light source 71 is disposed, is thicker, so as to improve the light entering efficiency from the light source.

The front light structure of the present embodiment does not have scattering characteristics during normal use when the light source is not turned on, and the illumination light from the light source is scattered and entered to the reflection type liquid crystal display panel side only when the light source is turned on for use in a dark place. Therefore, blurred and distorted characters and images on the display screen can be prevented in normal use, and contrast can be improved. Also a bright display screen can be implemented even in a dark place.

[Modification of Reflection Type Liquid Crystal Display Device with Front light Structure]

In the present embodiment, a reflection type liquid crystal display device having a front light structure as an illumination device is described.

FIG. 102 is a cross-sectional view depicting a reflection type liquid crystal display panel comprising a conventional front light structure. A polarizer 504 is formed on the surface of a liquid crystal panel 505, which has a reflection film and a liquid crystal layer inside, and a front light structure comprised of a light source 501, reflector 502 and a light guiding plate 503, is layered on the front. An air layer intervenes between the polarizer 504 and the light guiding plate 503.

Light from the light source enters the light guiding plate 503 as incident light 507A, which has some degree of spreading. The light guiding plate 503 is a prism where a sharp slope 503A and a mild slope 503B are combined, and the incident light 507A is guided in the light guiding plate 503 while being totally reflected on the mild slope 503B and the face 503C at the liquid crystal panel side. This light, which is totally reflected on the mild slope 503B, is also totally reflected on the shape slope 503A, advances to the liquid crystal panel 505 side, is reflected on the reflection face in the liquid crystal panel, and is emitted to the display side as light 507P. By this light 507P, the reflection type liquid crystal display panel can be used in a dark palace with no external light.

Actually however, reflection occurs at the interface 503C between the light guiding plate 503 and the air layer, or at the interface 504B between the polarizer 504 and the air layer, and the light 507Q, which does not transmit to the liquid crystal panel 505, leaks to the display side. Also, the light reflected at the sharp slop 503A of the light guiding plate 503 reflects on the interfaces 503C and 504B. It is also possible that light reflected inside the liquid crystal panel 505 reflects again on the interfaces 503C and 504B, reflects inside the liquid crystal panel 505, and this light 507S becomes the cause of a ghost image on the display. Normal external light also reflects on the interfaces 503C and 504B without transmitting to the liquid crystal panel 505, and leaks to the display side as light 507V.

In this way, in the case of a reflection type liquid crystal display panel with a conventional front light structure, there are many reflected light components which do not transmit to the liquid crystal panel and do not contribute to the display, therefore contrast drops considerably.

Therefore it is a first feature of the present embodiment that a low refractive index material, which can be formed at low cost, is disposed between the light guiding plate and the polarizer of the front light, so that normal light components which enter the liquid crystal panel are not reflected to the display side, while maintaining the light guiding components.

It is a second feature that a low refractive index material, which can be formed at low cost, is disposed between the touch panel and the light guiding plate of the front light, so that guided light does not enter the transparent conductive film while sufficiently controlling reflectance.

It is a third feature that a light shielding layer is formed at the sharp slope side of the prism faces of the light guiding plate via a low refractive index layer, so that leak light can be blocked without damaging the functions of the light guiding plate.

FIG. 90 is a cross-sectional view depicting a rough configuration of the reflection type liquid crystal display device of the fabrication example 1. This example has the above mentioned first feature where 501 is a cold cathode tube, 502 is a reflector, 503 is a light guiding plate, 504 is a circular polarizer, 505 is a reflection type liquid crystal panel, and 506 is a low refractive index layer.

The light guiding plate 503 is fabricated by press-molding acrylic resin with refractive index n=1.49. The surface of the light guiding plate 503 is comprised of a first inclined face 503B, which rises from a flat plane, or from a plane in parallel with the flat plane at a first angle, and a second inclined face 503A, which is adjacent to the first inclined face 503B, and which falls at a second angle which is larger than the first angle. As FIG. 90 shows, the incident face 503D and the plane 503C (the above mentioned flat plane) are almost perpendicular to each other, the plane 503C and the first inclined face 503B have a 2° angle, and the plane 503C and the second inclined face 503A have a 45° angle. The plane 503C and the first inclined face 503B may be in parallel (0°).

The circular polarizer 504 is comprised of a polarizer and λ/4 plate (returdation film), which are layered from the light guiding plate 503 side.

In this example, a low refractive index layer 506, comprised of fluorine resin material, is formed between the light guiding plate 503 and the polarizer 504 of the liquid crystal panel, so that the light guiding plate 503, the polarizer 504, and the liquid crystal panel 505 are integrated without intervening with the air layer. For the low refractive index layer 506 comprised of fluorine resin material, a sitop made by Asahi Glass, for example, is used, and this material has refractive index n=1.34. This fluorine resin material can be formed simply at low cost by dipping the press-molded light guiding plate 503 made of acrylic resin into a liquid material tank. This requires a much lower cost compared with the conventional fabrication method of AR-coating by a sputtering method, which has been proposed.

Light emitted from the cold cathode ray tube 501 enters the incident face 503D of the light guiding plate 503 via the reflector 502. Light 507A, which entered the light guiding plate, advances inside the light guiding plate as light which is ±42° with respect to the normal line of the platen 503D, that is, with respect to plane 503C. Of this light, the components which entered the mild slope 503B are totally reflected, and becomes components 507B and 507C which advance to the sharp slope 503A and the interface 503C. Light 507B is also totally reflected on the sharp slope 503A, and advances to the liquid crystal panel 505 almost vertically. In this case, the low refractive index layer 506 (n=1.34) has been formed between the interface 503C of the light guiding plate 503 and the interface 504B of the polarizer 504, so reflected light at these interfaces is considerably decreased, and most of the components advancing vertically enter the liquid crystal panel 505, and become light components to be used for the display. As a result contrast improves.

With the light 503C, components having an incident angle to the interface 503C of 64° or more are totally reflected and advance inside the light guiding plate again. With the light 507A, components advancing directly to the interface 503C are equivalent to the light 507C, so are separated into components which are guided according to the incident angle and components which enter the liquid crystal panel 505. Therefore, even if the low refractive index layer 506 (n=1.34) is disposed at the interface 503C of the light guiding plate 503 instead of a conventional air layer (n=1), the light guiding functions of the light guiding plate 503 are affected very little, and it is restrained that a light in the light guiding plate leaks to the display without entering the liquid crystal panel, and contrast drops.

Out of the components of the incident light advancing directly to the interface 503C, the components of light which incident angle to the interface 503C is 64° or less enter the liquid crystal panel 505 via the low refractive index layer 506 and the circular polarizer 504. There are, however, few such components. And these components become stray light due to the characteristics of the liquid crystal panel and polarizer, and do not contribute to the display.

External illumination light 507D enters from the light guiding plate 503, and illuminate the liquid crystal panel 505, but the light guiding plate 503, circular polarizer 504 and reflection liquid crystal panel 505 contact each other via the low refractive index layer 506. Since the refractive index of the low refractive index layer 506 is n=1.34, which is higher than the air layer, n=1, reflectance can be decreased at the interface. Therefore reflection by the light guiding plate interface 503C and the polarizer interface 504B, which have been a problem of conventional structures, can be considerably decreased. Therefore in the case of the liquid crystal panel used for this fabrication example, contrast improved dramatically, that is, when only a liquid crystal panel is used, contrast is 20, when the front light of a conventional structure is used, contrast is 5, and when the front light of the present invention is used, contrast is 12.

FIG. 91 is a cross-sectional view depicting a rough configuration of the reflection type liquid crystal display device of the fabrication example 2. This device also has the above mentioned first feature, and in FIG. 91, the same elements as the fabrication example 1 are denoted with the same numbers, and descriptions for this are omitted.

In the fabrication example 1, interface reflection is controlled by contacting all the elements, but in the present fabrication example, the light guiding plate part and the liquid crystal panel pair are separated, and an effect similar to the fabrication example 1 can be obtained.

As illustrated, the circular polarizer 504 is contacted with the light guiding plate 503 via the low refractive index layer 506. At this part, the light guiding functions and the reflectance control functions are the same as the fabrication example 1. However, the light component 507B, which emits from the light guiding plate at an angle close to vertical after reflecting to the interface 503A, and the illumination component 507D from the outside, have reflection components just like prior art due to the air layer in between when transmitting the circular polarizer interface 504B and the liquid crystal panel interface 505A.

However, in the present fabrication example, both the lights of the interfaces 507B and 507D transmit through the circular polarizer, then are reflected on the interfaces 504B and 505A, and enter the circular polarizer 504 again. At this time, incident light, which enters the circular polarizer 504 again, is absorbed by the circular polarizer, so reflected light is not leaked to the display side, and contrast does not drop as in prior art.

In the present fabrication example, a circular polarizer is used, which is a polarizer and the λ/4 plate (returdation film) which are bonded. For the λ/4 plate (returdation film), a normal λ/4 plate (returdation film) and λ/2 plate (returdation film) may be combined. In this case, combining is more effective since the tolerance, wavelength dependency and incident angle dependency of a λ/4 plate (returdation film) can be compensated by the λ/2 plate (returdation film).

FIG. 92 is a cross-sectional view depicting a rough configuration of the reflection type liquid crystal display device of the fabrication example 3. This example has the above mentioned second feature.

In this example, a transparent conductive film 508 is formed on the entire surface of the light guiding plate 503. In this transparent conductive film 508, a terminal for measuring potential is attached at a peripheral part (not illustrated), so as to function as a touch panel to perform coordinate input based on the potential change at each point. Details on the operation and principle of this touch panel are omitted here, since it is not related to the principle of the present invention. Other elements are almost the same as the fabrication example 1, and are denoted with the same numbers as the fabrication example 1, so descriptions thereof are omitted.

A problem when the touch panel and the reflection liquid crystal display device are integrated is that light in a specific band of the light, which is guided by the light guiding plate, is absorbed by the transparent conductive film 508. In other words, the transparent conductive film 508 absorbs the light components of blue and red, and green becomes dominant on the display face. However, both the light guiding plate of the front light and the touch panel must be disposed on the liquid crystal panel (observer side), and cannot have an optically independent configuration, in order to prevent a drop in display quality.

The present inventors examined structures where the reflection of display light and the external illumination light are controlled, where light which is reflected and advances in the light guiding plate does not pass the transparent conductive film, and they invented the present invention to dispose the low refractive index layer 506A contacting between the light guiding plate 503 and the transparent conductive film 508, just like fabrication examples 1 and 2. By using this structure, reflection by display light and external illumination light can be restrained while maintaining the light guiding components. In the present fabrication example, the low refractive index layer 506A is formed on the light guiding plate 503 by fluorine resin coating, then ITO film is formed by deposition so as to form the transparent electrode film 508. In the light guiding plate fabricated this way, components which entered from the light source to the light guiding plate partially pass through the low refractive index layer 506A, and reach the ITO layer 508. However, most components totally reflect at the interface between the light guiding plate 503 and the low refractive index layer 506A. Therefore the light components which leak to the ITO layer 508, which is the transparent electrode, decrease, and the conventional problem of absorbing blue and red light components in the ITO layer 508 is considerably improved, and the integration of the front light and the touch panel becomes possible.

In the case of a large display device, however, the absorption of blue and red components in the ITO film may be a problem, even with the configuration of the present fabrication example. This is because a part of the light which enters from the light source, as mentioned above, passes through the interface 503A, and reaches the ITO layer 508. Therefore the present inventors invented the following configuration as a countermeasure thereof. FIG. 93 shows an example.

As FIG. 93 shows, a dye layer 511 is intervened between the low refractive index layer 506A and the transparent electrode layer 508. The other parts are the same as FIG. 92. The dye layer 511 is contacted between the low refractive index layer 506A and the transparent conductive film layer 508, as illustrated. Since the ITO layer 508, which is the transparent electrode layer, absorbs 15% of the B band and 25% of the R band, the material of the dye layer 511 is selected to compensate this, to absorb 25% of the G band and 5-10% of the B band. By this, the components of all the RGB bands can be equally absorbed by the dye layer 511 and the ITO layer 508. Therefore green dominating the display face can be prevented. By this structure, the light reaching the transparent conductive film layer can be corrected by the dye layer, even if color balance is lost by the absorption of the transparent conductive film, the lost balance can be compensated by the dye layer 511, and a large touch panel integrated type display device can be implemented without dropping the display quality.

The front light of the touch panel integrated type can exhibit higher display quality by integrated with a circular polarizer and liquid crystal panel, just like the fabrication example 1 and 2.

Needless to say, a reflection film type touch panel is possible if a spacer and counter ITO substrates are added.